The present invention relates to a dispersant having excellent properties of dispersing organic and inorganic substances and an effect of remarkably improving the stability of the dispersion system. In particular, the present invention relates to a dispersant for a coal/water slurry which dispersant exhibits excellent effects of increasing the concentration and improving stability of the slurry when it is left to stand.
It is known that polystyrenesulfonic acid produced by sulfonating polystyrene and salts thereof are usable as antistatic agents, dispersants and various other agents. They are used as, for example, antistatic agents for papers [Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") No. Sho 57-53953], antistatic agents for resins [Japanese Patent Unexamined Published Application (hereinafter referred to as "J.P. KOKAI") No. Sho 59-8741], dispersants for coal/water slurry (J.P. KOKAI Nos. Sho 57-145187, Sho 62-590 and Sho 63-278997 and Japanese Patent Application No. Hei-1-338564), and dispersants for cements (J.P. KOKAI Nos. Sho 51-525, Sho 51-64527, Sho 56-41866, Sho 57-156355, Sho 60-46956 and Sho 63-25251). The polystyrenesulfonic acid and salts thereof are usually produced by polymerizing styrenesulfonic acid monomer or by sulfonating polystyrene. They have a structure shown by the following general formula (II) or the like: ##STR2## wherein l represents an integer and k represents 0 or an integer of at least 1. Although styrene of l recurring units in the above formula has one SO.sub.3 X group, some of the recurring units may have 0 or two or more SO.sub.3 X groups.
Although these known polymers exhibit an excellent effect for increasing the concentration of the dispersion system, their effect of improving the stability of the dispersion system is yet insufficient.